In recent years, the computer is being made to operate faster, and a semiconductor integrated circuit (IC) to be used is being integrated higher. To conform to the high integration of the IC, it is necessary to make the wiring patterns fine and to adopt a multilayered structure.
To adopt the multilayered structure, the unevenness of the wafer itself as the substrate and each layer of the multilayered structure must be made smaller than ever. If a step portion because of the unevenness becomes large, there is a possibility of various failures such as degradation in coverage (step coverage) on step portions when forming a film, a change in film thickness of the photoresist on the step portions in a lithography process, and the like. To avoid such problems involved in multilayering, a slurry is used to polish the semiconductor to further flatten not only the wafer as the substrate but also the surface of each layer formed on the wafer.
In a semiconductor polishing process, e.g., a wafer production process, an important process which has an influence on the surface roughness of the product wafer includes a polishing step. The polishing step is conducted by contacting the surface of a wafer adhered to a spindle to a polishing pad on the surface of a rotating table and rotating the rotating table while supplying a polishing slurry to the contact portion. The polishing slurry used in the polishing step has a polishing material dispersed in a solution, and colloidal silica, fumed silica or the like is used as the polishing material. And, an alkaline solution is sometimes used to provide an effect of chemically etching the wafer surface.
In the device production process, CMP (Chemical Mechanical Polishing) is used as a method of polishing the semiconductor to further flatten the surface of each layer when a metal wiring layer, an interlayer insulating film or the like is formed to have a multilayer lamination structure. This CMP is basically performed by an apparatus similar to the one used in the polishing step of the wafer production. The polishing material used here includes colloidal silica, fumed silica, fumed almina, precipitated alumina, ceria and the like. In the CMP process, an acid solution is sometimes used in order to provide an effect of chemically etching the metal layer and interlayer insulating films.
The semiconductor polishing slurry might have the inclusion of a very small amount of impurity metal ions, an impurity metal colloid, impurity metal hydroxide and the like such as iron, aluminum, copper, nickel derived from contamination or the like from the polishing materials, the polishing device or the atmosphere. As described in Japanese Patent Laid-Open Application No. Hei 11-186201, for example, when a silicon wafer or the like is polished with a semiconductor polishing slurry containing such impurity metal ions and the like, there is a problem that the polished wafer is contaminated by the impurity metal ions because copper, iron and nickel ions are particularly easy to spread in silicon. To avoid the problem, it is said necessary to control the concentrations of copper, nickel and the like in the polishing slurry to 0.01 to 1 ppb, respectively.
The semiconductor polishing slurry in the CMP process is attempted to be recycled in order to reduce a polishing material cost, an environmental load by decreasing a discharged liquid amount or a time for specifying various conditions involved in replacement of the polishing slurry. But, the fact is that the used semiconductor polishing slurry has an increased amount of tungsten, copper, aluminum and the like generated from the polished metal layer and the insulating films between the layers and is discarded without being recycled.
It is presumed that the impurity metal compounds contained in the semiconductor polishing slurry are present in various forms. It is because the semiconductor polishing slurry has a different pH depending on the types of the impurity metal compounds. That is the semiconductor polishing slurry also has a variable behavior depending on the types of metals, but the impurity metal compounds can be present in forms of, for example, ions, colloids or hydroxides depending on the pH of the semiconductor polishing slurry. Therefore, it is necessary to change a process of removing the impurity metal compounds depending on the forms of the impurity metal compounds present in the semiconductor polishing slurry.
Accordingly, it is considered to employ a method of recycling by removing a very small amount of metal ions in the polishing slurry and purifying. As one of purifying methods, it is considered to employ a method of capturing and removing metal ions by using an ion-exchange resin. This method has an advantage that the metal ions can be removed relatively easily, but because the ion-exchange group is a sulfonic acid group (sulfonyl group) or a carboxylic acid group (carboxyl group), it has a high pH dependency and very poor metal ion adsorption selectivity. Therefore, if there are alkali metal ion such as sodium ion or potassium ions, the ion-exchange resin has a disadvantage that the removal efficiency of other metal ions subject to the removal drops considerably. And, when the ion-exchange resin is used to purify the semiconductor polishing slurry, there is a problem that the polishing performance is largely affected because the pH of the purified polishing slurry changes depending on a type of the functional group fixed onto the resin.
In addition, Japanese Patent Laid-Open Application No. Hei 9-314466 proposes a method of removing heavy metals contained in a semiconductor wafer polishing slurry by using a chelate resin to improve the metal ion adsorption selectivity by improving the defect involved when the ion-exchange resin is used.
However, the chelate resin has a bead-like or particle-like shape which has a chelate functional group introduced into a polymer, such as styrene-divinylbenzene, which has a low polarity and a rigid three-dimensional crosslinked structure, and has a problem that a capturing rate of metal ions is low because a rate of diffusion into the bead-like or partile-like chelate resin required for selective separation of a very small amount of metals is slow. That is the semiconductor polishing slurry contains a high concentration of a polishing material and a pH adjuster up to several percent, so that the chelate resin developed in order to perform selective separation in a general water system is quite hard to remove by selectively separating a very small amount of ionic metals, colloidal metals or hydroxide metals from the semiconductor polishing slurry.
The present invention has been made in view of the above circumstances and provides a material for purification of a semiconductor polishing slurry that is capable of efficiently purifying the semiconductor polishing slurry by a simple process, for example, capable of not only preventing metal contamination of a semiconductor wafer or the like as effectively as possible without depending on an existing form of the metals but also achieving recycling of the polishing slurry without any problems, and a process for purification of a polishing slurry with the use thereof.
The present invention has been made to remedy the above-described problems and provides a material for purification of a semiconductor polishing slurry that without changing a pH, is capable of efficiently purifying the semiconductor polishing slurry by a simple process, to thereby not only prevent metal contamination of, for example, a semiconductor wafer as effectively as possible but also achieve recycling of the polishing slurry without any problems; a module for purification of a semiconductor polishing slurry; and a process for purification of a polishing slurry with the use thereof.